This editorial comments on the usefulness of the CASS study to the physicians seeing patients with cardiac disease. Despite the enormous amount of information thus far provided by the 24 million dollar CASS, utilization of its results will not be easy. CASS implies that the patient who has mild angina pectoris or who is asymptomatic after healing of AMI does not need CABG (or possibly percutaneous transluminal coronary angioplasty) at least at the present time. Because coronary bypass or dilatation is unnecessary in this asymptomatic or mildly symptomatic state, justification for angiography to determine the status of the coronary arteries and left ventricle is lacking. But, if angiography is not performed, the data acquired in CASS is really not applicable. If angiography is performed in the asymptomatic or mildly symptomatic patient, the finding of greater than or equal to 70% diameter reduction in greater than or equal to 2 major (excluding left main) coronary arteries may result, in probably many medical centers, in the performance of coronary bypass or dilatation. The major worry in avoiding the performance of cardiac catheterization would be the missing of severe (greater than or equal to 70% diameter reduction) narrowing of the left main coronary artery. But, severe left main narrowing was found in less than 2% of the more than 16,000 subjects screened for randomization. It therefore would appear most reasonable in light of CASS not to perform coronary angiography in the patient who has mild angina (with or without previous AMI which healed) or is asymptomatic after healing of AMI. When symptoms of myocardial ischemia appear or worsen, coronary (and left ventricular) angiography can then be performed with coronary dilatation and/or bypass thereafter if appropriate. A major implication of CASS, therefore, is to avoid the performance of coronary (and left ventricular) angiography until symptoms of myocardial ischemia become moderate or severe (as opposed to absent or mild) despite medical therapy.